PTT over Cellular (PoC) is a service defined by Open Mobile Alliance (OMA) for implementing group sessions on a packet-switched network. The PoC uses Voice over Internet Protocol (VoIP) and half duplex to implement real-time communication of the client efficiently at low costs. The PoC service is characterized as follows. Without dialing, the user can press a special key to implement voice communication; multicast is enabled, namely, one person speaks, and many persons listen; the group is defined beforehand or temporarily; a half duplex mode is applied in the conversation process, and the called party cannot speak while listening; and the client stays online, it takes a short time to set up a call, and the dialing is convenient.
The OMA gives an elementary definition of the network framework of the PoC. As shown in FIG. 1, the network framework includes a PoC client, a PoC server, a core network that supports SIP/IP (SIP/IP core), a PoC XML Document Management Server (XDMS), a presence server, a presence source, a watcher, a Document Management (DM) client, an XML Document Management Client (XDMC), a shared XDMS, an aggregation proxy, a DM server, an access network, and a remote PoC network.
The PoC function is primarily implemented by a PoC server and a PoC client. The PoC XDMS and the XDMC implement the PoC group information management operation. The PoC client implements signaling interaction with the PoC server under session control through a PoC-1 interface, a SIP/IP Core, and a PoC-2 interface, and implements media transmission through a PoC-3 interface.
Peer-to-peer communication runs when various devices on the same network communication level of a hierarchical architecture interact with each other.
In the existing PoC standard, media bursts carried over Real-time Transport Protocol (RTP) in a session, media burst control signaling, and quality feedback reports all pass through the PoC-3 interface and the PoC-4 interface. As shown in FIG. 2, in all session types, RTP media transmission is simplex. Therefore, at a specific moment, only one participant is allowed to initiate RTP media bursts. Both sent and received RTP media bursts pass through the controlling PoC server. Some PoC servers capable of forwarding (such as PoC Server A and PoC Server B in FIG. 2) are responsible for forwarding the RTP media bursts to the PoC server provided with the control function (CF), and then the CF PoC server distributes the media bursts to all PoC clients that participate in the session.
In the process of developing the present invention, the inventor detects at least these problems in the prior art. In the PoC standard and the service solution in the prior art, the media bursts generated by client talk bursts in a PoC service session are distributed by a PoC server capable of the CF to clients in a centralized way. Such a practice in the prior art brings these defects. The PoC server needs to distribute the media bursts received and generated by client talk bursts to other session participants, without allowing for impact on traffic transmission caused by the geographic area of the PoC client or for sufficient use of the terminal capabilities, whereas the PoC server bears a heavy load, and the network traffic near the PoC server is high, especially when the PoC 2.0 supports multimedia bursts and discrete media bursts (such as files).